The invention relates to an apparatus and a method of aligning an edge of a textile material web according to the preamble of the independent main claims.
When manufacturing textile workpieces, e.g. hand towels or bed linen, the edges of the material web to be processed are in many cases required to be aligned as precisely as possible. This is necessary particularly, but by no means exclusively, for hemming of a material web because it is only by feeding the edge as precisely as possible into the hemming device that a cleanly stitched hem may be obtained. As it is, in principle, immaterial to the application of the invention whether the material web is continuous or material portions cut to a specific length and/or width are to be processed, in the following only the generic term, material web, is used.
For aligning the edges of textile material webs, apparatuses are known from prior art, which comprise frictional wheels movable from below into frictional engagement with a material web in the region of its edges. The frictional wheels are in said case disposed in such a way as to be supported radially at a specific angle, e.g. 45xc2x0, to the conveying direction of the material web so as to be rotatable about an axis of rotation, with the result that at least a specific component of the applied frictional force acts at right angles to the conveying direction upon the material web. By means of the component of frictional force applied at right angles to the conveying direction the material web may be displaced at right angles to the conveying direction so that the edge of the material web may be aligned at right angles to the conveying direction, e.g. in dependence upon the rotational speed or the contact pressure of the frictional wheel.
A drawback of the known apparatuses for aligning the edges of a material web is that, in order to apply the frictional force, the material web has to be at least slightly pressed between the frictional wheel and an oppositely arranged counterpressure element, e.g. a pressure belt applied from above against the material web. The pressing of the material web between frictional wheel and counterpressure element impedes the actually desired alignment motion because the material web between frictional wheel and counterpressure element has to be pulled out at right angles to the conveying direction. Furthermore, the material web because of the impeding of the alignment motion in the region of the frictional forces, which are applied by the frictional wheel and directed at right angles to the conveying direction, has a tendency to form creases, which in particular may prevent trouble-free operation of hemming devices. With the known apparatuses and methods, moreover, materials which do not rest substantially in a completely crease-free manner on the work surface may not be aligned with the required accuracy and at the required speed. For instance, problems arise particularly when hemming materials having a creased ruched band.
From DE 200 09 773 an apparatus is known, by means of which particularly materials having a creased ruched band may be conveyed in a straightened form. To said end, the apparatus comprises contact pressure elements, which may be applied from above against the material and displaced synchronously with the conveying speed in the direction of the conveying motion.
The object of the present invention is to propose an apparatus and a method, by means of which the drawbacks of prior art are avoided when aligning the edges of a material web.
According to the invention, the apparatus is provided with at least one adjusting member, which may be applied from above against the material web in the region of an edge extending parallel to the conveying direction. Said adjusting member is displaced towards the work surface until the material portion is at least slightly pressed between adjusting member and work surface. As soon as the adjusting member rests against the material web, it is on the one hand displaced synchronously with the conveying motion of the material web parallel to the conveying direction so that the conveying motion of the material web in conveying direction is not impeded by the adjusting member. At the same time, for alignment of the edge of the material web the adjusting member may be displaced at right angles to the conveying direction so that the edge of the material web at the one side of the adjusting member is laterally offset at right angles to the conveying direction and at the same time the material web at the other side of the adjusting member curves up possibly with simultaneous formation of a longitudinal fold. In said case, depending on the stiffness of the material web used it may happen that the material web, particularly in the event of larger adjusting motions of the adjusting member, in the absence of support from below does not actually curve up but drops back into the plane of the work surface so as to form longitudinal folds.
The adjusting members may in principle be of any desired structural design. Particularly advantageous configurations arise when the adjusting members are structurally designed in accordance with the described contact pressure elements and disposed in the apparatus. In said case, it is naturally conceivable to use the contact pressure elements described in DE 200 09 773 and adjusting members according to the invention simultaneously in one apparatus.
The adjusting members according to the invention are particularly suitable for aligning material portions having special properties, such e.g. ruched bands. When the material portion to be aligned is composed of a plurality of materials, e.g. a smooth material having a ruched band stitched thereon, further adjusting members in addition to the adjusting members according to the invention may be provided in the apparatus. The edge of the material portion e.g. in the region of the ruched bands is then aligned by the adjusting members according to the invention and the additional adjusting member is used to align the edge of the smooth material. All adjusting members for aligning a material edge, such as are known from prior art, may be considered as an additional adjusting member.
According to the invention, a fixing of the material web in the region of the edges to be aligned, e.g. by means of pressure belts applied from above, is not absolutely essential prior to alignment of the edge. So that the edge to be aligned is prevented from slipping after alignment at the adjusting member and may therefore be conveyed even over extended distances in the required position to downstream work stations, e.g. a hemming device, it is particularly advantageous when the apparatus is provided with a fixing device, by means of which the position of the edge at right angles to the conveying direction may be fixed.
Said fixing device may be designed in a particularly simple manner as a continuous-loop pressure belt, which extends parallel to the conveying direction and which may be applied in conveying direction in the region downstream of the adjusting member from above against the material web so as to fix the position of the material web in the region of the aligned edge.
It is further advantageous when, for fixing the pressure belt against the aligned edge of the material web, use is made of a pressure roller, which presses the pressure belt in the direction of the work surface against the material portion.
For checking the position of the edge to be aligned upstream and/or downstream of the alignment at the adjusting member, position sensors may be disposed in the apparatus upstream and/or downstream of the adjusting member. Such position sensors are known from prior art and may be designed, for example, in the manner of inductive pickups or in the manner of one or more photoelectric barriers. In order to be able to align the material edge at any time automatically without intervention by minding personnel, a control and/or closed-loop control device may be provided on the apparatus. Said control and/or closed-loop control device receives, as input signals, the measuring signals of one of more position sensors disposed upstream and/or downstream of the adjusting member. In dependence upon the difference between a preset setpoint position of the edge to be aligned and the actual position measured upstream and/or downstream of the adjusting member, the control and/or closed-loop control device calculates control commands for setting the adjusting member. Which control or controller algorithms are used in said case depends on the respective application, the choice being in principle free. For example, P, PD or PID controllers may be used to correct the system deviation.
The use of the method according to the invention for alignment of the edge of a material portion is particularly advantageous when the edge, subsequent to alignment, is hemmed in a hemming device.
There now follows a detailed description of two embodiments of the invention which are illustrated in several drawings.